Upstream concepts to Adapt.jl and friends

[oschulz]

Reminder issue. Part of the concepts in HeterogeneousComputing should ideally be upstreamed to Adapt/ArrayInterfaceCore, KernelAbstractions and the GPU packages when ready.

See JuliaGPU/Adapt.jl#64 .

[vchuravy]

Looking at this I would be open to take these features on for KA 0.10/1.0

We are getting closer to having KA be used by GPUArrays to provide default implementations

[oschulz]

Thanks @vchuravy! I'll be very happy to "upstream" anything you like in here.

[oschulz]

I think we should still strive to have the basic definition of a compute unit (and of what you can do with it) in a very lightweight package, though. We should be able to do things like "move this data to where that data is" in a very generic fashion in packages without taking on heavy dependencies.

While KernelAbstractions isn't a very heavy package, it's not very lightweight either (partially due to StaticArrays :-) ) and packages that don't implement kernels probably won't want to depend on KA.